Download Salmonella Lecture

Typhoid/ Enteric fever
Dr. Jyotsna Agarwal
Professor, Dept. Microbiology
KGMU
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Salmonella
• Salmonella is Gram-negative,
rod-shaped
• Facultative anaerobe in family
Enterobacteriaceae
• Motile, Non lactose fermenting
• Over 2400 serotypes
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Faeco-oral transmission
Refrigeration does not kill bacteria, Heat at
600C destroys
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Clinical Syndromes of Salmonella
Salmonellosis = Generic term for disease
 Enteritis (acute gastroenteritis)
 Enteric fever (prototype is typhoid fever and
less severe paratyphoid fever)
 Septicemia (particularly S. choleraesuis, S. typhi,
and S. paratyphi)
 Asymptomatic carriage (gall bladder is the
reservoir for Salmonella typhi)
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Enteritis( Food Poisoning)
 Most common form of salmonellosis with
foodborne outbreaks and sporadic disease
 High infectious dose (108 CFU)
 Poultry, eggs, etc. are sources of infection
 6-48h incubation period
 Nausea, vomiting, nonbloody diarrhea, fever,
cramps, myalgia and headache common
 Many species of salmonella can cause this (eg. S.
typhimurium) except S. typhi
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Pathogenesis
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Bacteria penetrates intestinal cell in
ileocaecal region
Inflammatory response to bacterial
multiplication in the cell
Prostaglandins secreted
Increase in C-AMP
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Clinical Syndromes- Enteric fever
 S. typhi causes typhoid fever
S. paratyphi A, B and C cause milder form of
enteric fever called paratyphoid fever
 Infectious dose large = 106 CFU
 Fecal-oral route of transmission
 Person-to-person spread by chronic carrier
 Fecally-contaminated food or water
 Food handlers contaminate food
 10-14 day incubation period
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Virtually non existent in developed world
In developing countries endemic
Typhoid more common than paratyphoid
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Pathogenesis of Enteric fever
M cells on Peyers patches
Invade intestinal lining cells
bloodstream (primary bacteremia)
Phagocytosis
Transported (R E system), continue to replicate
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Pathogenesis
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contd…
Second week: re-enter bloodstream (secondary
bacteremia) endotoxemia
Second to third week: gallbladder, secreted in
bile, re-infect intestinal tract
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Complications: Intestinal haemorrhage,
perforation, cholecystitis
Less commonly: Bronchopneumonia,
arthritis, osteomyelitis
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Epidemiology & Clinical Syndromes
Asymptomatic Carriage
 Chronic carriage in 1-5% of cases following S.
typhi or S. paratyphi infection (Temporary
carrier>12 months shedding)
 Gall bladder usually the reservoir
 Chronic carriage with other Salmonella spp.
occurs in <<1% of cases and does not play a
role in human disease transmission
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Early 1900- Mary Mallon
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Virulence factor
•Encapsulation , antigenic mimicry, masking
•Evasion or incapacitation of phagocytosis
• Mechanisms enabling an invading
microorganism to resist being ingested and lysed
by lysosomes
intracellular survival and multiplication
•Endotoxin
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Diagnosis of Typhoid Fever
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Clinical:
For Lab diagnosis, specimen & diagnostic tests
according to duration of fever:
Blood for Culture
WIDAL
Stool culture
Urine culture
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Blood Culture
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In blood culture bottle
Repeated cultures may be required
Subculture on MacConkey medium (NLF colony)
Clot culture- put clot in blood culture bottle, lyse it with
streptokinase in B/C bottle
Use serum for WIDAL
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Selective media for subculture from blood
culture bottle: MacConkey, Wilson Blair,
Tellurite blood agar
Enrichment broth for culture of stool/urine:
Selenite F broth, Tetrathionate broth
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Serological test- WIDAL
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For detecting antibody
Agglutination test
Endemic titre
Paired sera
For carriers - antibody against Vi antigen
Rapid test- Typhi dot
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Treatment, prevention & control of
salmonella infections
Enteritis:
 Antibiotics not recommended for enteritis
because prolong duration
 Control by proper preparation of poultry & eggs
Enteric fever:
 Antibiotics- Chloramphenicol, cipriflox,
Ceftriaxone
 Identify & treat carriers of S. typhi & S. paratyphi
 Vaccination can reduce risk of disease for
travellers in endemic areas
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Salmonella vaccines
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TAB: Salmonella typhi, paratyphi A &B, killed whole
cell
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Oral Ty21-A: Live attenuated, Salmonella typhi
vaccine
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Vi capsular polysaccharide vaccine
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Summary- Enteric fever
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S. typhi / S. paratyphi
Mode of spread /Pathogenesis
Clinical features / Complications
Laboratory diagnosis
Treatment/vaccines
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